This application claims the benefit of the filing date of German Patent Application No. 101 64 299.7 filed on Dec. 28, 2001 pursuant to 35 U.S.C. 119 and the Paris Convention.
The invention concerns a microwave oven system.
Microwave ovens which may be for example in the form of chamber-type ovens, through-type or continuous ovens and the like are usually operated by means of at least one magnetron or a number of magnetrons, operating at a given frequency. The frequency involved is usually 2.5 GHz. The operating frequency may also be for example 915 MHz.
Crucial factors in regard to the heating output power produced in an element of volume of a material to be heated in a microwave oven are the electrical field strength "Egr" of the microwave field, the operating frequency f, the loss factor tan xcex4 and the relative dielectric constant xcex5. The following applies in regard to the volume power density P:
P=2xcfx80fxc2x7xcex5xc2x7tan xcex4xc2x7"Egr"2. 
The volume power density is therefore proportional to the operating frequency of the at least one magnetron used in the microwave oven.
German utility model No 1 818 464 describes a microwave oven of through-flow type with an elongate working chamber which is closed at all sides in respect of high frequency and with a conveyor belt extending through the working chamber for the material to be treated in the microwave oven. During its transportation movement through the oven the material passes successively through various microwave fields at different frequencies. It will be appreciated that this is a through-flow oven having a plurality of magnetrons operating at different frequencies in the direction of transportation movement of the material to be treated in the oven.
Consideration may be given to U.S. Pat. No. 3,494,722 disclosing a method and an apparatus for sterilisation by means of microwave radiation. In that case the microwave radiation can be at a wavelength in a range of between 0.9 and 17 GHz. A preferred wavelength is between 2.36 and 2.9 GHz, the usual operating frequency being 2.45 GHz.
U.S. Pat. No. 4,746,968 describes an apparatus for drying material by means of microwave radiation in combination with infrared radiation. The microwave radiation has for example an operating frequency of 2.54 GHz or 915 MHz.
DE 196 43 989 A1 discloses an apparatus for treating substances with electromagnetic high-frequency energy. That apparatus operates with magnetrons having an operating frequency of between about 100 MHz and 10 GHz, being supplied from mains units with a low degree of ripple or pulsation. In particular the apparatus involves the use of a microwave device, that is to say a magnetron, operating at a frequency of 2.45 GHz.
In all the known microwave furnace systems outlined above the or each respective magnetron has a given operating frequency in order to achieve the respectively desired heating power and activity.
An object of the present invention is to provide a microwave oven system which affords a high level of operational versatility without involving structural complications.
Another object of the present invention is to provide a microwave oven system in which it is very easily possible to alter the heating power as desired without the need for major electrical and/or mechanical changes at the microwave oven or peripheral equipment thereof such as a mains unit.
In accordance with the principles of the invention the foregoing and other objects are attained by a microwave oven system comprising at least one magnetron which has given electrical operating parameters such as anode voltage, heating voltage and heating current, and a mains unit for the at least one magnetron. The at least one magnetron of a given operating frequency is replaceable by a magnetron of another operating frequency. The magnetrons of the various operating frequencies are of at least similar or identical mechanical mounting dimensions. The mains unit can be used unchanged for the various magnetrons of different operating frequencies without a change in the electrical operating parameters. It will be noted that very minor alterations may possibly be required, in which respect the essential components of the system such as the heating and high-voltage transformers are retained unchanged.
In accordance with the invention therefore it is advantageously possible for example to replace a magnetron operating at a frequency of 2.45 GHz by a magnetron and launcher of an operating frequency of 915 MHz or 5.8 GHz in order to achieve the respectively desired heating effect. In that situation the respective magnetron and launcher only need to be simply removed from the microwave oven and replaced by the respectively desired other magnetron. As the magnetrons involving the different operating frequencies are of at least substantially the same mechanical dimensions, replacement of a magnetron of a given operating frequency by a magnetron of another frequency can be effected easily and without taking up a great deal of time. A microwave oven system in accordance with the invention therefore enjoys for example the advantage that, in the case of an existing microwave oven with magnetrons for example of an operating frequency of 2.45 GHz, those magnetrons can be replaced by magnetrons for example of an operating frequency of 5.8 GHz. The user of an already existing microwave oven therefore does not have to procure a different new microwave oven if he requires a different heating power, but he only needs to replace the existing magnetrons by magnetrons which involve the appropriate operating frequency. A quite considerable advantage in that respect is also that the mains unit of the existing microwave oven does not need to be replaced, but the existing mains unit can still continue to be used without change or only a few components are required for adaptation purposes in that respect.
In accordance with the invention it is possible for the at least one magnetron to be provided on the corresponding microwave oven directly, that is to say without a further microwave coupling device. If for example the at least one magnetron is combined with a coupling device it has then proven to be desirable in the microwave oven system according to the invention if the magnetrons of the various operating frequencies are combined with respectively associated microwave coupling devices. This means that, when replacing a unit consisting of a magnetron involving a given operating frequency and the associated microwave coupling device thereof, that unit is removed from the microwave oven and another unit consisting of a different magnetron with its associated microwave coupling device can then be easily fitted to the microwave oven. That procedure is simple and does not take up a great deal of time.
Further objects, features and advantages of the present invention will be apparent from the description of a preferred embodiment hereinafter.